New thermal runaway solution has nothing to do with cell chemistry.

LG Chem has developed a new flame-retardant plastic to combat thermal runaway in EV batteries. (Source: LG Chem.)

When lithium-ion (Li-ion) batteries go bad, they go really bad. Smoke, vapor, fire and explosion are all potential safety hazards in Li-ion applications, and engineers must take every precaution to prevent them.

Last month, LG Chem announced a new precaution for engineers to deploy. The company says it is developing an advanced plastic capable of preventing the spread of fire in electric vehicle (EV) batteries.

EVs are expected to play a key role in combatting climate change. Thanks to rapid developments in battery technology—particularly Li-ion batteries—the global EV market is growing exponentially.

However, despite fueling the EV transition, Li-ion batteries present a fire risk in the event of thermal runaway, the leading cause of EV fires. Regulators around the globe have imposed strict safety requirements on Li-ion batteries used in the transportation sector.

Thermal runaway is the Achilles’ heel of Li-ion batteries, a challenge that remains inherent to the chemistry. Lithium reacts violently with water, so putting out a Li-ion battery fire is not easy. LG Chem’s new plastic aims to stop such fires in their tracks.

LG Chem says in its press release that it spent “more than ten years of dedicated research” developing its new flame-retardant plastic. Designed for use in EV battery components, the plastic is made from several composites including polyphenylene oxide and polyamide resin.

Polyphenylene oxide is an amorphous engineering thermoplastic used in applications that require high heat resistance and dimensional stability, such as electrical components, automotive parts and medical instruments. Polyamide resins are opaque, high-density polymers with excellent strength and heat properties. Unlike other polymers, PA tolerates high temperatures and is strong enough to be used as a replacement for some metal components.

According to LG Chem, its new plastic product has superior properties for battery applications. The company’s tests revealed that the plastic can prevent the spread of flames “for over ten minutes at 1,000°C, 10 times longer than general plastics.”

EV occupants could use those extra minutes to evacuate their vehicles in the event of thermal runaway.

LG Chem says it is in the process of patenting its new plastic in Korea, the United States, and some European markets. The company plans to begin commercial production of the plastic in 2023.

While a boon for battery safety, LG Chem’s new plastic does not directly solve the problem of thermal runaway itself.

In lithium-ion batteries, thermal runaway is triggered when the amount of heat generated in a cell exceeds the amount of heat being dissipated. The accumulated heat raises the battery’s temperature, which results in an exponential increase in the battery’s reaction rates. This can cause an uncontrolled chain reaction with nearby cells and ultimately lead to combustion.

Various factors can cause thermal runaway, including battery overcharging and over-discharging, internal and external short circuits, high ambient temperature, rapid cycling, battery age, and mechanical deformation. EV batteries in particular are exposed to vibrations and mechanical shocks that can precipitate thermal runaway. A vehicle collision, to take the most extreme case, could critically damage the battery separator, causing an internal short circuit and leakage of the flammable electrolyte, leading to fire.

Effective thermal management is the main protection against battery thermal runaway.

A crucial part of any high-capacity Li-ion battery system, the battery management system (BMS) is responsible for providing stable battery operation, thermal management and protection against battery overcharging and over-discharging.

The materials and components used in a battery are also important factors in protecting against thermal runaway. The components should be chosen to dissipate heat, absorb shock and vibrations, and serve as a flame retardant and isolator if necessary, preventing cell-to-cell thermal runaway propagation. In EV applications, the materials must also be lightweight and not add excessive bulk to the size-constrained battery system.

Despite the many ongoing efforts to improve battery chemistries and structures, sometimes solutions can be found outside the cells themselves. Though LG Chem’s new battery plastic is not yet on the market, it and materials like it can help provide a barrier to battery catastrophe.